Variation of thermal stratification, first and second law efficiency due to the use of porous media in hot water tank

ABSTRACT

Thermal energy storage tanks are one of the widely used energy storage systems. In these systems, thermal stratification and energy storage capacity are the most important parameters affecting system performance. In this study, a porous medium was placed in the upper part of the tank, where the water in the tank is the hottest, in order to increase the system performance for standby mode. Thus, convection-induced movement of the water in the upper part of the tank was tried to be minimized and it was aimed to reduce the temperature drop. The results were determined experimentally in terms of first law and second law efficiency, maximum temperature difference, and overall heat transfer coefficient over a 48 hours cooling period. The porous media thickness was used as a parameter and its values were chosen as 10, 12, 14, and 16 cm. The best results were obtained for the porous media thickness of 16 cm, at which thermal stratification, first law, and second law efficiency increased by an average of 1.8 times, 1.6%, and 2.3%, respectively.

KEYWORDS:

• Thermal stratification
• first law efficiency
• second law efficiency
• thermal tank

Nomenclature

A	=	area, m2
c	=	specific heat capacity,J/kgK
E	=	energy,W
Ex	=	exergy,W
m	=	mass,kg
Po	=	atmospheric pressure,kPa
R	=	measured dimension quantity
u	=	internal energy,J
v	=	specific volume,m3/kg
s	=	entropy,J/ oC
T	=	temperature,oC
t	=	time,s
Q	=	energy, W
W	=	uncertainty in the measurement
$W_R^{+}$	=	total uncertainty associated

Greek symbols

${\eta }_{ı}$	=	first law efficiency,%
${\eta }_{ıı}$	=	second law efficiency,%

Subscripts

av	=	avarage
loss	=	loss
max	=	maximum
min	=	minimum
i	=	instantaneous
in	=	initial
o	=	ambient

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

Raw data were generated at [facility name]. Derived data supporting the findings of this study are available from the corresponding author [initials] on request.

Additional information

Funding

No funder was used in the realization of the study.